Regionless multiple label scintillation counting

Abstract

Apparatus and a regionless method of ascertaining the activity of each radionuclide in a dual-label sample. A set of correlation curves is generated utilizing quench standards for both a low energy radionuclide and a high energy radionuclide. A test sample was then counted and the quench-indicating parameters for the test sample are compared with the quench-indicating parameters of the correlation curves to determine the appropriate contribution of each radionuclide to the overall energy spectra of the test sample. From this comparison the overall count rate for the test sample may be allocated between a low energy radionuclide and a high energy radionuclide. By dividing the count rates by efficiencies determined from another set of correlation curves the actual disintegration per minute (DPM) rate for each radionuclide may be ascertained.

I claim: 
     
       1. A liquid scintillation counting system for use with a test sample containing one or more radioactive nuclides together with a liquid scintillator such that the disintegration rate for each radionuclide may be ascertained as a function of the pulse energy distribution spectra of the sample and known standards which comprises: transducer means for converting the energy released by the decay of the radionuclides into electrical pulses proportional thereto;   signal processing means connected to said transducer means for eliminating pulses which do not fall within a predetermined time differential window thereby screening out pulses which are not related to the decay of a radionuclide;   quantizing means connected to the signal processing means for converting each pulse into a representative digital signal; and   processing means connected to receive the digital signals from the quantizing means, said processing means including storage means for storing correlation curves between a first quench-indicating parameter and a second quench-indicating parameter and between the second quench-indicating parameter and efficiency for selected radionuclides and said processing means storing data representative of a second quench-indicating parameter of the test sample and the pulse energy distribution spectrum generated by the decay of the radionuclides in the test sample, and said processing means including means to determine the relative contribution of each radionuclide to the pulse energy distribution spectrum of the test sample and the actual disintegrations per unit time for each radionuclide in the test sample.   
     
     
       2. The apparatus as set forth in claim 1 wherein the processing means stores and processes the digital signals used to determine the first quench-indicating parameter and the second quench-indicating parameter without grouping the signals by energy regions. 
     
     
       3. The apparatus as set forth in claim 1 wherein the means to determine the relative contribution of each radionuclide to the pulse energy distribution spectrum uses a parameter based on pulses generated over the entire spectrum monitored. 
     
     
       4. The apparatus as set forth in claim 3 wherein the first quench-indicating parameter is the Spectral Index of the Sample (SIS) and the second quench-indicating parameter is the Spectral Index of the External Standard (SIE). 
     
     
       5. The apparatus as set forth in claim 1 wherein the second quench-indicating parameter is the endpoint of the higher energy radionuclide. 
     
     
       6. The apparatus as set forth in claim 4 wherein the means to determine the relative contribution of each radionuclide to the energy contribution solves the following simultaneous equations: ##EQU2## wherein SIS H  is the Spectral Index of the Sample for a higher energy radionuclide; SIS L  is the Spectral Index of the Sample for a lower energy radionuclide;   SIS T  is the Spectral Index of the Sample for the test sample;   CPM T  is the counts per minute from the test sample;   CPM H  is the counts per minute from the higher emergy radionuclide;   CPM L  is the counts per minute from the lower energy radionuclide; and wherein SIS H , SIS L  and SIS T  are determined based on the stored correlation curves and the measured SIS of the test sample.   
     
     
       7. The apparatus as set forth in claim 6 wherein the means to determine the actual disintegrations per unit time includes means for determining the efficiency of the appropriate radionuclide by comparing the stored correlation curve with the measured SIE of the test sample and thereafter by solving the following equations:   DPM.sub.L =CPM.sub.L /Eff.sub.L       DPM.sub.H =CPM.sub.H /Eff.sub.H     wherein DPM L  =disintegrations per minute for lower energy radionuclide;   Eff L  =efficiency of lower energy radionuclide;   DPM H  =disintegrations per minute for higher energy radionuclide; and   Eff H  =efficiency of higher energy radionuclide.   
     
     
       8. The apparatus as set forth in claim 1 wherein the first quench-indicating parameter is a measure of the first moment of the sample such as the Spectral Index of the Sample (SIS), wherein the second quench-indicating parameter is an external source quench-indicating parameter such as the Spectral Index of the External Standard (SIE), and wherein the means to determine the relative contribution of each radionuclide to the overall pulse includes means for determining the relative proportions between a point determined by the measured SIS and SIE of the test sample and the correlation curves for each radionuclide at the same SIE value. 
     
     
       9. The apparatus as set forth in claim 8 wherein the means to determine the relative contribution soles the following equations:   CPM.sub.L =(A/C)·CPM.sub.T       CPM.sub.H =(B/C)·CPM.sub.T     wherein CPM L  =counts per minute for the lower energy radionuclide;   CPM H  =counts per minute for the higher energy radionuclide;   CPM T  =counts per minute for the test sample;   A=distance from the measured point to the SIS correlation curve for the high energy radionuclide;   B=distance from the measured point to the SIS correlation curve for the low energy radionuclide; and   C=A+B=distance between the SIS correlation curves of the low and high energy radionuclides.   
     
     
       10. A regionless method for ascertaining the unknown quantity of multiple known radioactive nuclides in a test sample which comprises the steps of: establishing a first set of correlation curves between a first quench-indicating parameter and a second quench-indicating parameter for each of the known radionuclides;   storing a second set of correlation curves between the second quench-indicating parameter and efficiency for each of the known radionuclides;   determining a second quench-indicating parameter and a count rate for the test sample;   comparing the second quench-indicating parameter of the test sample to the first set of correlation curves to determine the relative proportions that each radionuclide contributes to the count rate for the test sample;   ascertaining the efficiency for each radionuclide by comparing the measured second quench-indicating parameter of the sample to the second set of correlation curves; and   calculating the unknown quantity of each radionuclide by dividing the proportional count rate for the radionuclide by the efficiency value for the radionuclide from the step of ascertaining.   
     
     
       11. The method as set forth in claim 10 wherein the step of establishing includes the first quench-indicating parameter being the Spectral Index of Sample (SIS) and the second quench-indicating parameter being an external source quench-indicating parameter such as the Spectral Index of the External Standard (SIE). 
     
     
       12. The method as set forth in claim 11 wherein the step of determining includes measuring the SIS and SIE values for the test sample and the step of comparing further comprises comparing the SIS value of the test sample to the SiS value of a higher energy radionuclide and a lower energy radionuclide at the same SIE value to determine the relative proportions of each radionuclide in the test sample. 
     
     
       13. The method as set forth in claim 12 wherein the step of comparing further comprises determining the count rate for each radionuclide by solving the following equations: ##EQU3## wherein SIS H  is the Spectral Index of the Sample for the higher energy radionuclide; SIS L  is the Spectral Index of the Sample for the lower energy radionuclide;   SIS T  is the Spectral Index of the Sample for the test sample;   CPM T  is the counts per minute from the test sample;   CPM H  is the counts per minute from the higher energy radionuclide; and   CPM L  is the counts per minute from the lower energy radionuclide.   
     
     
       14. The method as set forth in claim 13 wherein the step of calculating the unknown activity of each radionuclide further comprises calculating the actual disintegrations per minute (DPM) for each radionuclide by solving the following equations:   DPM.sub.L =CPM.sub.L /Eff.sub.L       DPM.sub.H =CPM.sub.H /Eff.sub.H     wherein DPM L  =disintegrations per minute for the lower energy radionuclide;   Eff L  =efficiency of the lower energy radionuclide;   DPM H  =disintegrations per minute for the higher energy radionuclide; and   Eff H  =efficiency of the higher energy radionuclide.   
     
     
       15. The method as set forth in claim 10 wherein the step of establishing a first set of correlation curves further comprises establishing the endpoint of the higher energy radionuclide as the second quench-indicating parameter. 
     
     
       16. The method as set forth in claim 12 wherein a measured point is determined by the measure SIS and SIE of the test sample, and the step of comparing further comprises solving the following equations:   CPM.sub.L =(A/C)·CPM.sub.T       CPM.sub.H =(B/C)·CPM.sub.T     wherein CPM L  =counts per minute for a lower energy radionuclide;   CPM H  =counts per minute for a higher energy radionuclide;   CPM T  =counts per minute for the test sample;   A=distance from measured point to SIS correlation curve for high energy radionuclide;   B=distance from measured point to SIS correlation curve for low energy radionuclide; and   C=A+B=distance between SIS correlation curves of low and high energy radionuclides.   
     
     
       17. The method as set forth in claim 10 wherein the step of determining further comprises determining a second quench-indicating parameter for the test sample over the entire energy range for the known radionuclides.